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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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366                                ALASKAN GLACIER STUDIES
the ice mass was separated from the main glacier. The size of the trees between Learnard and Portage Glaciers preclude the possibility that this detached ice remnant was supplied by Portage Glacier.
The Learnard Glacier has continued to melt back for the last twelve years, for while in 1909 the terminus was dark with debris, in 1898 it was white ice. The detached ice mass, however, has changed very little since 1898, for Mendenhall and Glenn described it vividly, in language which in all essential respects depicts the 1910 conditions. Yet that it is slowly wasting away is proved by its irregular surface, due to slumping and by the almost complete absence of vegetation on its surface. To show the conditions in 1898, we give Mendenhall's description, then that of Glenn, which furnishes a few additional items.
"This little glacier illustrates very well the rapidity of the ice retreat and shows us the processes whose results only remain in portions of the New England landscape. One quarter of a mile out from its present terminus is a hillock 220 feet high and half a mile long, with its longer axis parallel with the glacier front. It is now separated from this latter by an open valley paved with bowlders. At first sight this elevation was supposed to be a simple terminal moraine, but upon examination it proved to con-•sist mostly of ice deeply covered with angular d6bris, which is also disseminated through it. This remnant of the glacier seems to stand near a position which the ice front occupied long enough to become covered by a sufficiently thick mantle of protective d£bris, so that melting was not so rapid as in the less well-protected part of the glacier just back of the front. The separation from the glacier was probably facilitated by the exit of the subglacial stream through a tunnel back of the protecting mantle. The combined melting from above and below soon removed this neck, leaving the former front isolated as it stands today. Since its isolation it has been shrinking each summer, and now occupies less than half of its original area. Around its seaward side is a belt of rough ground of slight relief covered with angular and unsorted material, which has been let down into position by the melting of the ice front. The outer rim of this, zone is somewhat higher than the inner portion, giving it the form of a shallow amphitheater facing the remnant of the glacier which remains. The stability of the position of maximum advance for a short time due to the balance between flow and melting at the front accounts for the slightly greater accumulation there and the building of the low rubble wall.
These recent glacial details of topography are the more striking since they are built upon a smooth water-laid deposit of relatively fine material. This delta is of the type which usually forms before glaciers in these fiords, and gives about the only level areas to be found near sea level in a region of sharp topographic forms. At its outer margin a short distance seaward from low-tide level, the delta slopes abruptly to the profound depths so often found 14 these inlets."
Glenn states that in 1898 the stagnant ice block consisted of a "detached or isolated hill not far from tide-water, and contains not to exceed 2 acres of surface on its top. It is surrounded at a distance of from 30 to 50 yards from its base with a pile of rocks or bowlders, which evidently marks its original size. From this circle this moraine has gradually receded for a number of years, due to the action of the elements. Within thiq circle of bowlders others have been deposited, but in no regular order. The top and sides of this moraine are covered with a collection of dirt and stones to a depth